The invention relates to a specially prepared chromatographic sheet with adsorbent layer favorably used in pressurized layer chromatographic apparatuses, for the development of linear chromatograms.
Layer chromatography, which is liquid chromatography in a planar arrangement, is a method whereby a mobile phase (the solvent composite) travels on the stationary phase (the adsorbent layer) and carries one or several substances at varying speeds. By the layer chromatographic process, chemical compounds are preferentially adsorbed in an increasing molecular weight sequence onto the solid adsorbent material (the stationary phase). This adsorption is made possible by the solvent (the mobile phase) eluting adsorbed materials from the adsorbent. The distribution of the travelling compounds along the path of the solvent allows the separation of the chemical compounds.
One drawback of classical layer chromatography is the long developing time. Another drawback is that, due to the short length of the adsorbent layer, the separation is not perfect and the theoretical number of plates is limited.
Significant progress was made by the development of high-performance thin-layer chromatography (HPTLC) (see A. Zkatkis and R. E. Kaiser: High Performance Thin-Layer Chromatography, Elsevier, 1977), which, contrary to the classical layer chromatography, results in better dissolution in shorter developing times and shorter distances.
However, the most up-to-date technique is the so-called pressurized (sealed) layer chromatography (Hungarian Patent No. 173,749) which is realizable equally well on thin and thick layers, and provides the fastest separation. The essential step in the technique of pressurized layer chromatography is the application of an overpressure in a closed system to achieve a flow velocity of the solvent (mobile phase) over the adsorbent layer (stationary phase). The adsorbent layer is completely covered suitably with elastic foil, which is pressed in a cushion-like manner against the adsorbent layer by the application of external pressure. The cushion pressure (2-10 bar) should always be higher than the flow pressure (1-8 bar) of the solvent composite. In this so-called pressurized ultramicron chamber a separation can be attained within a very short time (1-10 minutes) which is better than that attainable in the earlier known chromatographic methods utilizing a planar arrangement. An apparatus was constructed for the development of both the concentric and linear chromatograms.
However, the following fundamental problems exist in the linear alternative of the pressurized layer chromatography as a result of the overpressure: (1) the solvent composite escapes at the edges of the adsorbent layer and (2) the front of the solvent flow is not straight, but rather is concentric, semicircular, or arc-shaped following solvent admission, e.g., in case of solvent admission at one point.